Harmonic generator



H. A. ROBINSON HARMONIC GENERATOR Aug. 28, 1956 2 Sheets-Sheet l Filed Oct. 25, 1951 Aug` 28, 1956 Filed Oct. 25. 1951 H. A. ROBINSON HARMONIC GENERATOR 2l Sheets-Sheet 2 VTT/m @gia L' Vm Pff-41. /Him MaJ- INVENTOR ATTORNEY United States Patent C HAnMoNrc GENERATOR HanrgsAeRubinson, Philadelphia, Pa., assigner, by mesne assignments, to the United StatestolAniericay asrepre.u sentedcby the :Secretaryo the Air Force.

Application O'ctolierZS, 11951, Serial'No. 253,141

7 Claims. (Cl. Z50-36)' This `invention relates to a harmonic generator, and more` particularly to. a harmonic generator which hasr special utility in connection` with a` multichannel' frequency generating system.

Recently, there has been developed a radio communication transmitter-receiver which makes` available for` frequency selection any one frequency channell of`44,000 which a'respaced'SOU cycles apartthrougli the frequency range of2` rnc. to 2`4mc. For such a transmittenreceiver, a-` 44,'0`0`-channel frequency `generator with a very high frequency stability is required. Such a generator includes.

fed a crystal-controlled.stable .frequency and the` output of this. discrimihat'orA controlslthe master. oscillator. In the harmonic' generators mentioned, any one of a number of harmonics ofa lower frequency sourcemay be selected dependentupon the' channel selection switch setting,

The proper operation 'of a frequencykgenerator ofthe type described requires the maintenance of a certain signal level* at the phasediscriminator, and `isbased on the presence of a constant signal level for' allV mixers: This is so because each mixer develops a numberA of spurious frequencies' if the signal: input level thereto rises. orfalls from'a standard or normal" value; Itis offcourse desirable in` a frequency generator' of' this type, for accurate frequency control, that the spuriousfrequencies out of the mixers be minimized; this requires `that the'input signal levelto such mixers 'be maintained substantiallyconstant;

Therefore, `anl objectY of this invention is to` devise' Aa tunable harmonie generator which providesl a substantially constant output level over awide range of selected harmonics. u

Another 'object is' to provide'a circuit-arran gement which compensates for the natural decrease amplitude'withincrease in harmonic number ofthe output of a harmonic frequency generator.

A` further object' `isto devise a` circuit arrangementl for a: harmonic generator which permits theAVC' circuit of thegenera'tor to functionmore ei'e'ctively, thus yproviding a' morenearly` constant outputtffom the generator;

Thel foregoing and other objects ofi the invention will be bestunderstood fromY lthe'- following description `of an exemplifi'cati'on thereof, reference being had. to` the `'accompanyingdrawin'gs, wherein: t

Fig;v 1i isf a schematic'representation ofacircui't'accord# ingto-this invention; andl` Figsi 2B and` 2C are harmonic frequency spectra useful inexplainingfthe'inventionz The output of the nal' Patented .Aug.. 28 1956 Theobjectssof thisinvention are accomplished;`brie1l-yv,

in the following manner: An inductance-capacitancerest tude `of the higher frequency. harmonics appearing-across.Y

the oscillatory circuit,`which isin the outputof'a harmonic generator stage.

Ina typicalfrequency generator ofthe 44000fchannel. type previously discussedQthere are three harmonic generators, suppliedwithSOO kc.,.5'0 kc. :md5 kc. respectively. By way of example, the 50.0 kc. harmonic generator will be described. Referring `to Fig. l, the SIlOflc. input. is

'supplied from afxed frequency source, such as a crystalcontrolled" oscillator, through. a coupling capacitor` 1. to the control grid' 2` of .a pentode vacuum tube 3. which functions as aharmonic. generator. A grid leak resistor 4` i's connected' from the grid side of f capacitor 1 to ground. The suppressor grid'of tube 3 is tied to its cathode, which.` is grounded. The screen gridof tube 3 is supplied through. the usual resistor 5' from the positive terminal. ofthe unidirectionall potential source. and is provided withl the usual" bypassing, capacitor 6. The anode 7 ofA tube 3 is connected` to a parallel tuned oscillatory circuit 12` including, a capacitor 8 and, in shunt thereto, a variable inductance `the total inductance value ofy whichu may be selected and changed iny discrete steps by means ofl the switch 9` which is a channel selection switch and' which engages any selected. one of a plurality of' xed contacts (in the actual embodiment built, these were twenty-two in number) connected to different portions of a single inductance or to different induct'ances which are connectedl in series with each other. To complete theY tuned circuit 12, the upper end of the single inductance or the upper one. ofthe several inductances is connected to the anode 7" andthe upper plate of capacitor 8, while. the movable armofLthe 22p'ositi`on switch 9 is connected to the lower plate ofcapacitor'S' and1 also through a resistor 1'0 to theV positive source 'to supply anode potential to tube 3; A bypassY capacitor 11 is connected from the lower plateof capacitors to ground. l

The tube 3with vits circuit'described functibnsas a har'- monic generator 'and ldevelopsa harmonicspectrum suchas illustrated* Fig. 2A, inwhich frequency or harmonic number is plotted; against harmonic generator output. It will' be" seen from this figure; as indicated by the dotted lineA yjoining thelendsr ofthe several spectral linesthat the voltage `outputr of the harmonic generator so far `described decreasesA asthe frequency or harmonic number increases.

In a particular embodiment oflhis invention, as'previously indicated; the switch Sl had twenty-two positions'. Any particular one `of the 6th through 27th harmonicsrof the 500 kc. input could then bev selected `by operation ofv this switch, `which means thatthe'output frequency range of the harmonic generator which was utilized extended from 3 mc. to 13.5` mc., a frequency ratioof 4.5: l. Over thi'sflargefrange of harmonic frequencies, as may be seen fromFig. 2A, the harmonic `frequency spectrum generated by the harmonic generatorincluding tube 3, andi appearing across the tuned outputif circuit 1li (including capacitor 8 and the switchable inductance orinductances) as switch 9p is moved, is rathernonuniform as4 regards amplitude,

the harmonic generator output falling ol in amplitude as higher frequencies or higher harmonic numbers are selected. An objective of this invention is to furnish relatively constant excitation to the grid of a mixer tube to be later referred to, for any desired harmonic selected by the operation of switch 9.

In the conventional circuit, the selected harmonic output voltage across tuned circuit 12, in which circuit harmonics of the 500 kc. fundamental input frequency appear, is coupled by a coupling capacitor and a conventional grid resistor to excite the grid of a second vacuum tube stage which constitutes `a harmonic amplifier. An AVC arrangement including a diode, provided with socalled de1ay, is coupled to receive a portion of the output of this second stage, to rectify it and to apply the rectified voltage as a control grid bias to the second stage. In this conventional coupling arrangement including the coupling capacitor and grid resistor, the use of a delayed AVC diode for the purpose of obtaining constant grid drive to the following mixer stage is ineffective for two reasons, one because there is inherently a very wide variation in amplitude of harmonic frequency output from the second stage resulting from the variation in grid drive for this stage which is illustrated in Fig. 2A, and the other because the AVC arrangement must operate by bias variation on a grid (the grid of the second stage or amplifier) which is already over-driven and developing considerable self-bias, particularly on the stronger lower order harmonics.

According to this invention, the desired substantially constant signal level at the grid of the mixer, which follows the second stage of the harmonic generator, is obtained by using a series inductance-capacitance coupling network between tuned circuit 12 and the control grid 13 of the second stage tube 14, the grid drive for the second stage tube 14 being taken from across the inductance of this network. y More particularly, with reference to Fig. 1, the anode '7 and the upper end of circuit 12 are connected through a capacitor 15 to the control grid electrode 13 of a pentode vacuum tube or electron control device 14 which constitutes `a harmonic amplifier. One end of an inductor 16 is connected to control grid 13, while the opposite end thereof is connected through a parallel RC filter network, consisting of a resistor 17 and a capacitor 1S, to ground. The cathode 19 'of tube 1d is grounded, while the network 17, 18 has a very low impedance at the harmonic frequencies. Therefore, the lower end of inductance 16 is held essentially at ground potential for harmonic frequencies, so that the effective grid drive (between grid 13 and cathode 19) for tube 14 is taken from across the inductance 16.

The inductance 16 and capacitor 15 together form a series inductance-capacitance (LC) network which is resonant at a selected frequency (for example, 19 mc.) which is considerably higher than the frequency of the highest harmonic desired to be utilized. in this way, and by control of the Q of inductor 16, the series network 15, 16 serves as a peaking circuit and has an output/input characteristic of the type illustrated in spectrographic form in Fig. 2B, the dotted line B joining the ends of the several spectral lines indicating that the ratio of output to input of the peaking circuit rises or increases as the frequency or harmonic number increases. The ratio of peaking circuit output to peaking circuit input might be termed gain, so that the peaking circuit 15, 16 has a rising gain-versusfrequency characteristic as illustrated in Fig. 2B.

The rising characteristic of Fig, 2B (which is applicable to the peaking circuit 15, 16 which is directly coupled to the harmonic generator output appearing in circuit 12) tends to compensate or counteract the falling generator output-versus-frequency spectrum characteristic of Fig. 2A, which latter characteristic represents the naturallcss in amplitude of the higher frequency harthus forming a capacitive voltage divider.

monies produced by the first harmonic generator stage including tube 3 and circuit 12.

In general, `with the resonant frequency of 15, 16 considerably higher than the frequency of the highest harxnonic desired from the tuned circuit 12, the resultant drive voltage V1 applied to the grid 13 of the second stage tube 14 may be maintained substantially constant in amplitude with frequency and of considerably lower amplitude as compared to the conventional capacitorresistor coupling. The resultant voltage V1 is plotted against frequency or harmonic number in spectrum fashion in Fig. 2C. As indicated by the dotted line C joining the ends of the several spectral lines, the drive voltage V1 is substantially constant or invariable with frequency or harmonic number.

The suppressor grid of tube 14 is connected to cathode 1 9, while the screen grid 20 of this tube is connected through a resistor 21 to the positive potential source, a bypassing parallel RC network consisting of resistor 22 and capacitor 23 being connected between grid 20 and ground. The anode or output electrode 24 of tube 14 is connected to a parallel tuned circuit 27 including a capacitor 25 and, in shunt thereto, a variable inductance the total inductance value of which may be selected and changed in discrete steps by means of the switch 26 which is ganged with switch 9, which is also a channel selection switch and which engages any selected one of a plurality of fixed contacts (in the actual embodiment built, these were twenty-two in number) connected to different portions of a single inductance or to different inductances which are connected in series with each other. To cornplete the tuned circuit 27, the upper end of the single inductance or the upper one of the several inductances is connected to the anode 24 and the upper plate of capacitor 25, while the movable arm of the 22-position switch 26 is connected to the lower plate of capacitor 25 and also through a resistor 28 to the positive source to supply anode potential to tube 14. A bypass capacitor 29 is connected from the lower plate of capacitor 25 to ground.

The tube 14 with its circuit described functions as a harmonic amplifier to amplify and further select the particular harmonic supplied to control grid 13.

Switch 26, like switch 9 and ganged therewith, has twenty-two positions and may function to select any particular one of the 6th through 27th harmonics of the 500 kc. input, which means that the range of frequencies in the lead connected to anode 24 may be from 3 mc. to 13.5 mc., las indicated.

The anode 24 and the upper end of circuit 27 are connected through la coupling capacitor 30 to one input grid 31 of a mixer tube 32, while the movable arm of switch 26 is connected through a capacitor 33 to this same grid, The cathode 34 of tube 32 is connected to ground through a biasing network consisting of a pair of series-connected resistors 35 and 36 across which is connected a capacitor 37. A resistor 38 is connected from grid 31 to the common junction of resistors 35 and 36. It is the grid excitation voltage V2 of mixer tube 32 which is maintained relatively constant by the circuit of this invention. The voltage V2 is that supplied to grid 31 relative to ground. In other words, according to this invention the harmonic generator output Vz driving the mixer grid 31 is maintained substantially constant for any selected harmonic.

A delayed AVC arrangement including a diode 39 is coupled to the output of the second stage 14. A connection extends from anode 24 of this stage through a coupling capacitor 40 to the anode 41 of diode 39. The rectified voltage from diode 39 is fed through resistor 42 to the lower end of inductance 16, being filtered by 17 and 13. The rectied voltage is applied via 16 to control grid 13 of the second stage as an AVC bias therefor. Delay for this AVC arrangement is provided by biasing the cathode 43 of diode 39 positively with respect to its anode. Aflpair-ofresistor'sf41and45tareiconnected in series between..l the v positive- :terminal: off ther'unidirectional source and ground to constitute a voltage divider, the cathode 43 being connected tothejunction pointofjtliese two resistors.. Resistor '45is"b'ypassed by. capacitor `46 Tlietypeof excitationdescribed'for grid 13 of.1 thesecond stage, using the peaking'circuitvlS, 16, `permitsth'e effective functioning of' the delayed. AVC arrangement since both of` the limitations previously. discussed have been corrected. Moreparticularlygi th'e variation .in grid drive with frequency furthe' secondstage 14 hasJbeen made almostnil (see Fig." 2C), resultingin substantially no varlation in amplitude witlfrequencyof output' from thisstage. Also; theAVC arrangem'entoperates' by bias variation on grid 13 which is not now over-driven (see the rather low amplitude of drive voltage V1 in Fig. 2C) and which is therefore not developing self-bias. Since the delayed AVC is now permitted to function very effectively, the harmonic generator output voltage V2 driving the mixer grid 31 is substantially constant with frequency. Stated in another way, the output level from the twostage harmonic generator of this invention is substantially constant over a wide range of selected harmonics.

Another input grid 47 of mixer tube 32 is supplied from a suitable source of signals, which for example may Ilie in the frequency range of 1.9 mc. t0 12.9 mc. In a multichannel frequency generating system of the type previously referred to herein, the signal supplied to grid 47 may be derived from the master (controlled) oscillator. A resistor 48 connects grid 47 to ground.

The remaining grid 49 of tube 32 is connected through a resistor 50 to the positive terminal of the unidirectional potential source and is provided with a bypass capacitor 51. The anode 52 of this tube is connected through a resistor 53 to the grid end of resistor 50.

Mixing of the two frequencies supplied to tube 32 takes place in such tube, resulting in the production of a beat frequency voltage at anode 52 which may vary anywhere from 600 kc. to 1100 kc. as channel switching takes place.

Although the invention is not to be deemed limited in any Way thereby, the following component values are given by way of example. These were the values used in a circuit built according to this invention and successfully tested in operation.

Tube 3- Type 5840. Tube 14 Type 5840. Tube 32 Type 5636. Tube 39 Type 5896. Resistor 4 330,000 ohms. Resistor 5 180,000 ohms. Resistor 10 4,700ohms. Resistor 17 220,000 ohms. Resistor 21 47,000 ohms. Resistor 22 22,000 ohms. Resistor 28 4,700 ohms. Resistor 35 470 ohms. Resistor 36 220 ohms. Resistor 38 470,000 ohms. Resistor 42 100,000 ohms. Resistor 44 120,000 ohms. Resistor 45 2,200 ohms. Resistor 48 470,000 ohms. Resistor 50 4,700 ohms. Resistor 53 22,000 ohms.` Capacitor 1 47 mmfd. Capacitor 6 5,000 mmfd. Capacitor 8 100 mmfd. Capacitor 11 5,000 mmfd. Capacitor 15 18 mmfd. Capactor 18 10,000 mmfd. Capacitor 23 5,000 mmfd. Capacitor 25 47 mmfd.

What is claimed is:

1f Incombination; an electron coutrolldevice amplifyingstagethedeviceof wh`ich"lias` aicontrolV electrode and output' electrodes, a tunablecircuit wherein harmonics of a' fundamentalV frequency. appear, means for adjustablytuningsaid"cir'cui`t"to any one offa plurality ofpredetermined harmonics ofisaidfundamentalfrequency, a res- "f onant network haviuga resonanefrequency higher than,

the frequency of the highestone oftsaidplurality oflhar.- monic fequencies, means coupling` said. network. to wsaid circuit, `meansl for applyinggthe voltage appearing across` only a portion of'saidinetwork to said control electrode, means coupled to said output electrodes for rectifying a portion of the output of said stage, and means for applying the rectified voltage to said control electrode as an AVC voltage for said stage.

2. In combination, a tunable circuit wherein `harmonies of a fundamental frequency appear, means for adjustably tuning said circuit to any one of a plurality of predetermined harmonics of said fundamental frequency, an inductance-capacitance resonant network having a resonant frequency higher than the frequency of the highest one of said plurality of harmonic frequencies, means coupling said network to said circuit, and means for utilizing the voltage appearing across solely the inductance of said network.

3. In combination, an electron control device amplifying stage the device of which has a control electrode and output electrodes, a tunable circuit wherein harmonics of a fundamental frequency appear, means for adjustably tuning said circuit to any one of a plurality of predetermined harmonics of said fundamental frequency, a series resonant `network having a resonant frequency higher than the frequency of the highest one of said plurality of harmonic frequencies, means coupling said network to said circuit, means for applying the voltage appearing across only a portion of said network to said control electrode, means coupled to said output electrodes for rectifying a portion of the output of said stage, and means for applying thc rectified voltage to said control electrode as an AVC voltage for said stage.

4. In combination, an electron control device amplifying stage the device of which has a control electrode and output electrodes, a tunable circuit wherein harmonics of a fundamental frequency appear, means for adjustably tuning said circuit to any one of a plurality of predetermined harmonics of said fundamental frequency, a series inductance-capacitance resonant network having a resonant frequency higher than the frequency of the highest one of said plurality of harmonic frequencies, means coupling said network to said circuit, means for applying the voltage appearing across solely the inductance of said network to said control electrode, means coupled to said output electrodes for rectifying a portion of the output of said stage, and means for applying the rectified voltage to said control electrode as an AVC voltage for said stage.

5, In combination, a tunable circuit wherein harmonics of a fundamental frequency appear, means for adjustably tuning said circuit to any one of a plurality of predetermined harmonics of said fundamental frequency, a seriesconnected inductance-capacitance resonant network having a resonant frequency higher than the frequency of the highest one of said plurality of harmonic frequencies, means coupling said network to said circuit, and means for utilizing the voltage appearing across solely the inductance of said network.

6. In combination, a tunable circuit wherein harmonics of a fundamental frequency appear, a series-connected 7 i 8 inductance-capacitance resonant network having a res- References' Cited in the file of this patent onant frequency higher than the frequency of the highest UNITED STATES PATENTS harmomc appearing 1n said c1rcu1t whlch 1s desired to be I utilized, means connecting said network directly in par- 116781199 Retenmeyer July 24 1928 allel to said circuit through connections having low im- 210821517 Rust m' Tune 11 1937 5 2221086 Foster Nov. 12 1940 pedance at sald harmonlc frequencies, and means for 1 1 1 utilizing the voltage appearing across solely the induce 212541114 Wllsof Aug 261 1941 ance of said network 2,384,263 Schleslnger Sept. 4, 1945 one of said plurality of harmonic frequencies, means conneoting said network directly in parallel to said circuit through connections having low impedance at said harmonic frequencies, and means for utilizing the Voltage appearing across solely the inductance of said network. 

